Cell surface antigens mediate a range of interactions between cells and their environment. These interactions include cell-cell interactions, cell-surface interactions and cell-solute interactions. Cell surface antigens also mediate intra-cellular signalling.
Cells are characterised by qualitative and quantitative differences in the cell surface antigens expressed. Qualitative and quantitative changes in the cell surface antigens expressed alter both cell function (mode of action) and cell functionality (action served).
Being able to effect qualitative and/or quantitative changes in the surface antigens expressed by a cell has diagnostic and therapeutic value. Transgenic and non-transgenic methods of effecting qualitative and/or quantitative changes in the surface antigens expressed by a cell are known.
Protein painting is a non-transgenic method for effecting qualitative and/or quantitative changes in the surface antigens expressed by a cell. The method exploits the ability of GPI linked proteins to spontaneously anchor to the cell membrane via their lipid tails. The method described in the specification accompanying international application no. PCT/US98/15124 (WO 99/05255) includes the step of inserting a GPI linked protein isolated from a biological source into a membrane. Isolated GPI-anchored proteins are stated as having an unusual capacity to reintegrate with a cell-surface membrane.
Cells exist in an aqueous environment. The cell membrane is a lipid bilayer that serves as a semi-permeable barrier between the cytoplasm of the cell and this aqueous environment. Localizing antigens to the cell surface may also be achieved by the use of glycolipids as membrane anchors.
The method described in the specification accompanying international application no. PCT/NZ02/00214 (WO 03/034074) includes the step of inserting a controlled amount of glycolipid into a membrane. The amount of glycolipid inserted is controlled to provide cells with a desired level of antigen expression.
The method described in the specification accompanying international application no. PCT/NZ03/00059 (WO 03/087346) includes the step of inserting a modified glycolipid into a membrane as a “membrane anchor”. The modified glycolipid provides for the localisation of antigens to the surface of the cell or multicellular structure. New characteristics may thereby be imparted on the cell or multicellular structure.
These methods typically include the isolation of a glycolipid or glycolipid-linked antigen from a biological source. The isolation of glycolipids or glycolipid-linked antigens from biological sources is costly, variable and isolatable amounts are often limited. Obtaining reagents from zoological sources for therapeutic use is particularly problematic, especially where the reagent or its derivative products are to be administered to a human subject.
Synthetic molecules for which the risk of contamination with zoo-pathogenic agents can be excluded are preferred. Synthetic counterparts for naturally occurring glycolipids and synthetic neo-glycolipids have been reported. However, for a synthetic glycolipid to be of use as a membrane anchor it must be able to spontaneously and stably incorporate into a lipid bi-layer from an aqueous environment. The utility of synthetic glycolipids in diagnostic or therapeutic applications is further limited to those synthetic glycolipids that will form a solution in saline.
Organic solvents and/or detergents used to facilitate the solubilization of glycolipids in saline must be biocompatible. Solvents and detergents must often be excluded or quickly removed as they can be damaging to some cell membranes. The removal of solvents or detergents from such preparations can be problematic.
Damage to cell membranes is to be avoided especially where the supply of cells or multicellular structures is limited, e.g. embryos, or the cells are particularly sensitive to perturbation, e.g. hepatocytes.
There exists a need for water soluble synthetic molecules that are functionally equivalent to naturally occurring glycolipids and glycolipid-linked antigens in respect of their ability to spontaneously and stably incorporate into lipid bi-layers, including cell membranes.
Providing such synthetic molecules would obviate the limitations of glycolipids and glycolipid-linked antigens isolated from biological sources and facilitate being able to effect qualitative and/or quantitative changes in the surface antigens expressed by a cell.
It is an object of this invention to provide such synthetic molecules and a method for their preparation. It is a further object of this invention to provide synthetic molecules for use in diagnostic and therapeutic applications. The preceding objects are to be read disjunctively with the object to at least provide the public with a useful choice.